a2ui

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The vocabulary layer for A2UI — useful for humans · declarative for agents.
The model names an atom. The renderer compiles the HTML, CSS, SVG, and animation.

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Independent, unofficial catalog — not affiliated with or endorsed by Google. A2UI is Google's protocol; the official spec lives at a2ui.org.

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The idea

Rather than asking an agent to generate custom UI every turn — expensive, fragile, unpredictable — give it a stable vocabulary of atoms and let it compose from those.

Raw HTML   609 tok  ████████████████████████████████████████
OpenUI     287 tok  ███████████████████
A2UI        68 tok  ████

Fewer tokens to describe the same UI. The model names an atom; the renderer expands it into the full HTML server-side, and that expansion never re-enters the model's context window. (The efficiency framing here is still being validated — see benchmarks/BENCHMARK.md for the current methodology.)

Work in progress. The atom vocabulary itself is stable; what it's for is still being explored. The live catalog and this repo are the vocabulary and its renderers — applying that vocabulary to new use cases (rendering a CLI's own output, for instance, in a sibling project not yet published) is ongoing, not finished.

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Connect an agent

The catalog is consumable three ways, no signup for any of them — BYO by design: renders happen in your environment, your data never touches us.

Channel	Endpoint	What an agent gets
MCP server	a2uicatalog.ai/mcp	Tools to browse catalogs, validate/compose payloads, emit render URLs, and render live views on MCP Apps hosts
ARD manifest	/.well-known/ai-catalog.json	Agentic Resource Discovery — every atom as a crawlable, typed entry
Machine catalog	a2uicatalog.ai/spec.json	The full schema in one fetch — types, fields, surface compatibility, degradation notes

5-minute quickstarts: Claude (Desktop / claude.ai) · Gemini Enterprise (BYO-MCP)

As an agent skill — this repo ships a SKILL.md, so any agent using the skills ecosystem can pick up the catalog's when-to-use guidance directly:

npx skills add a2uicatalog/a2ui@a2ui-atomic-catalog

A few atoms, live on the site — click through to a full spec + fields table for each:

<table> <tr> <td align="center"><a href="https://a2uicatalog.ai/atoms/glowing_stat/"><img src="examples/atom-glowing-stat.png" width="240" alt="glowing_stat atom preview"></a><br><a href="https://a2uicatalog.ai/atoms/glowing_stat/"><code>glowing_stat</code></a></td> <td align="center"><a href="https://a2uicatalog.ai/atoms/stat_card/"><img src="examples/atom-stat-card.png" width="240" alt="stat_car